Telephone system



T. ZUSCHLAG TELEPHONE SYSTEM April 10,1928. 1,665,683

Filed Oct.v 6, 1924 Patented Apr. 10, 1928.

UNITED STATS PATENT OFFICE.

THEODOR ZUSGHLAG, OF NEW YORK, N. Y., ASSIGNOR TO SIEMENS & HALSKE, .AKTIEN- GESELLSCHAET, OF SIEMENSSTADT, NEAR GERMANY.

BERLIN, GERMANY,'A CORPORATION OF TELEPHONE SYS'IIEM.

Application filed October 6, 1924, Serial No. 742,038, and in Germany October 6, 1923.

This invention relates to telephone systems and more particularly to balancing networks which are employed in connection with such systems.

In balancing networks such as are commonly employed in connection with hybrid coils at repeater stations, and junction points between two-wire and four-wire lines, it is frequently found that at certain frequencies, the impedance of the artificial line or balai'icing network differs from the impedance of the transmission line, and consequently current may flow in the bridge circuit at these frequencies.

It is an object of this invention to eliminate the flow of current in the bridge circuit of a system such as described above at these frequencies as well as at other frequencies.

The above object and others which will be apparent as the nature of the invention 1s disclosed are accomplished by connecting one of the branch transmission lines associated with the bridge circuit to a second bridge circuit consisting of impedances so designed that at frequencies for which the original bridge circuit is unbalanced the second bridge circuit is balanced and will prevent current flow.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the claims appended hereto, the invention itself, as to its objects and advantages, the

mode of its operation and the manner of its organization will be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof in which;

Fig. 1 shows diagrammatically a common type of bridge circuit such as is used in telephone repeater stations; A

Fig. 2 illustrates a double bridge circuitconstructed in accordance with this invention and V r Fig. 3 shows a series of curves to be used in explanation of the operation of the system shown in Fig. 2.

Referring more particularly to Fig. 1, an incoming transmission line A is connected to local lines B and O in conjugate relationship by means of hybrid coil U and'balancing network K. In such a'system transmission may occur from line A to line B and from line C to line A but, for all frequencies at which ond bridge connection is obtained the impedance of balancing network K equals the impedance of line A, transmission will not take place between lines B and C. If, however, the impedances of line A. and network K are not exactly balanced, a differential effect is produced by means of which signals may be transmitted between lines B and C. I

This undesired transmission between lines 0 and B is prevented in the system illustratedin Fig. 2 in which portions similaivto those shown in Fig. l are given the same reference characters. In this circuit a secloy impedances It and \V which are connected to line B in series with the secondary of the hybrid coil, the balanced bridge comprising the two halves of the secondary of the hybrid coils and iuipedances 1t and W. These impedanccs must be so chosen that for those frequencies-for which the impedances of the line A and artificial line K show small orno difl'erenccs at all, the difference of the impedances It and IV is large, and vice versa. It is assumed that the particular frequencies, the transmission of which between C and B is prevented by the second bridge c0nnection mentioned above, are not necessary to insure good speech transmission between A and B, as this bridge connection also prevents transmission of these frequencies from denser, and for impedance W a parallel connection of inductance and capacity of suitable magnitudes.

I In Fig. 3 curves W represent the impedance of network W plotted as a function of the frequency and curve It represents the impedance of the network R plotted to the same coordinates. In the condition illustrated-by these curves, impedances R and W are equal at high frequencies which means that at those frequencies at which signals would tend to be transmitted between lines B and C such transmission is prevented by the balanced condition of the second bridge including impedances R and W.

If the line A and the artificial line K show impedance deviations at frequencies below the speech frequency region, the impedance B should consist of an inductance and im- 7 pedance W should consists of an inductance and a capacity connected in parallel. By

connecting resistances in series or in parallel with the impedances afurther balance at any desired frequency may be obtained.

Although this invention has been shown and described-as applied to a particular system operating in a specific manner, it is not to be limited thereto but only in accordance with the scope of the invention as defined by the following claims:

What is claimed is:

1. In a communication system, a two-way transmission line, a pair of one-way transmission lines, means interconnecting said lines so that transmission is permitted between said two-way line and each oneway line, but transmission is prevented between said one-way lines at certain frequencies, in combination with a. balanced bridge circuit connected in one of said one-way lines and at all times operative to prevent transmission between said one-way lines at other frequencies.

2. A combination in accordance with claim 1 in which the arms of said bridge circuit include elements the impedance of which differs at different freque ncies to produce a balance in said bridge circuit at frequencies at which said means is ineffective to prevent transmission between said one-way lines.

3. In a communication system, a twoway transmission line, a pair of one-way transmission lines, means for connecting said two-way transmission line to said one way lines including a hybrid coil having windings and a balancing network for said" said lines comprising a hybrid coil and a balancing network, said network being designed to simulate the impedance of said two-way transmission line at certain frequencies whereby at those frequencies transmission between said .onc-way lines is prevented, and additional meansvfor preventing transmission between said one-way lines at other frequencies comprising a bridge circuit consisting of a pair of, impedance networks, said last networksbeing of equal impedance at those frequencies at which the two-way transmlssio-n line and the first mentioned network are of unequal impedance.

5. In a communication system, a transmission line and a balancing'artificial line therefor, a pair of local lines associated with said first line in balanced relationship including a transformer having split primary -75 and secondary windings, a pair of 1mpedances connected in series with said secondary windings, said impedances being so designed that they are equal at frequencies at which the impedance of the transmission line and artificial line differ, and that they are unequal at other frequencies.

In testimony whereof-I alfix my signature.

THEO. ZUSOHLAG. 

